f(x) = 2x + c, g(x) = cx + 5, fg(x) = 6x + d. c and d are constants. Work out the value of d. 3 marks.
fg(x) = 2(cx+5) + c
= 2cx+10+c [1 mark]
fg(x) = 6x+d. fg(x) = 2cx+10+c
6x = 2cx and d = 10+c [2 marks]
3 = c and therefore d = 13 [3 marks]
HK
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